1. Field of the Invention
The present invention relates to pneumatic tires, and in particular to high-performance pneumatic tires which are capable of enhancing wet performance and reducing pattern noise compatibly without adversely affecting the primary properties of the tire.
2. Description of the Prior Art
In order to improve wet property and reduce pattern noise, for example, it is generally known to select a tread pattern having a combination of straight circumferential grooves and directional (uni-directional) slant grooves. In this case, it is effective to increase the negative ratio, which is the ratio of total groove area to the sum of total groove area and total land area.
However, since a conventional pattern comprising a combination of straight circumferential grooves and slant grooves has large circumferential groove portions and small slant groove portions, problem exists in that the appropriate distribution of grooves across the tread in the widthwise direction of the tire is not obtained and hence drainage efficiency is not effectively enhanced. Further when the negative ratio is increased to enhance the wet property, the land area is small and the necessary land rigidity is not retained, resulting in other problems of decreasing resistance to wear and cornering property, in addition to degrading pattern noise.
The present invention has been accomplished based on the realization that directional slant grooves having a small slant angle with respect to the circumferential direction of the tire is advantageous with respect to wet property, while when only these slant grooves are arranged, it is difficult to retain sufficient land rigidity resulting in degraded steering stability and the effect on reducing noise by pitch-variation is small because of the decreased number of pitches.
The objects of the present invention are to provide a pneumatic tire having enhanced wet property and effectively reduced pattern noise without degrading primary functions such as steering stability and resistance to wear by selecting the position and angle of such slant grooves, combining other slant grooves having selected position, angle and width with these slant grooves, and defining the distribution of the negative ratio across the tread in the widthwise direction of the tread.